Middle-aged and older women whose diets contained the most trans fats in the newly reported study had the highest risk for stroke, but regular use of aspirin appeared to moderate this risk.
Researchers analyzed data collected from more than 87,000 women in the largest study ever to examine the impact of dietary fat on stroke risk.
They found no evidence linking total fat intake or intake of other types of fat to stroke, but eating high amounts of trans fats was strongly associated with elevated risk.
Women in the study who ate the most trans fats had a 39% greater stroke risk than women who ate the least after taking into account other lifestyle and dietary factors that contribute to stroke.
"Trans fats are well-recognized risk factors for heart disease and heart attack, and our study finds that they are a risk factor for ischemic stroke," says researcher Ka He, MD, MPH, of the University of North Carolina at Chapel Hill. An ischemic stroke occurs when the supply of blood to a region of the brain is fully or partially blocked.
Trans Fats and Stroke
Once a staple of processed baked goods and fried foods, trans fats are slowly disappearing from grocery aisles and restaurant kitchens as a growing number of studies suggest that they may be more dangerous for health than other dietary fats.
The new study, which appears in the March issue of the journal Annals of Neurology, included women participating in the ongoing Women's Health Initiative (WHI) health trial.
The women, who were aged 50 to 79 when they enrolled in WHI in the mid-to-late 1990s, completed detailed dietary questionnaires, which, among other things, examined their intake of various dietary fats.
The finding that trans fat consumption, but not consumption of other fats, was strongly associated with increased stroke risk was only seen in women who were not regular aspirin users.
The study suggests, but does not prove, that eating a diet high in trans fats increases stroke risk and that regular aspirin use may help lower this risk, he tells WebMD.
Because people who eat a lot of trans fats tend to eat poorer diets overall, some other dietary factor may explain the association, says nutrition expert Nancy Copperman, MS, RD, who is director of public health initiatives at the North Shore-LIJ Health System in Great Neck, N.Y.
"A diet that is high in trans fats also tends to be high in sugar, sodium, and other unhealthy things," she says.
Because about 85% of the women enrolled in the trial were white, it is also not clear if the findings apply to women of other ethnicities.
CDC: Trans Fat Blood Levels Dropping
But Copperman says the evidence as a whole suggests that efforts to get trans fats out of the foods we eat are warranted.
And those efforts appear to be having an impact.
A recent CDC-funded study suggests that in the U.S., average blood levels of trans fats have plummeted in recent years, dropping by almost 60% between 2000 and 2009.
"The legislation banning trans fats and manufacturers' voluntary efforts to remove them from their products have had an impact," Copperman says. "But consumers still have to be vigilant and read labels."
She adds that if that label contains the words "partially hydrogenated" -- which means the product has trans fats -- leave it on the grocery shelf.